A base station apparatus of performing a handover (HO) processing when a mobile station (hereinafter referred to appropriately as “user equipment (UE: User Equipment)”) located in the own cell moves to a neighboring cell of another base station while maintaining a data communication, etc. in a mobile communication is conventionally known (for example, see Non-Patent Literatures 1 and 2).
In order to respond to a recent rapid increase of traffics, for example, in a mobile communication system of the LTE (Long Term Evolution) scheme, a demand for a small-cell base station (hereinafter also sometimes called as “small base station”, “Home eNB”, or “HeNB”) having a cell radius that is further smaller than a cell radius of a conventional macro-cell base station (hereinafter also sometimes called as “MeNB”) and pico base station (hereinafter also sometimes called as “PeNB”) is increasing. As a result of starting services by this mobile communication system of the LTE scheme, it has become possible to perform a high-speed data communication and to provide various services.